## **Core Concept**
Isoniazid is a critical component of the antitubercular therapy, especially in the DOTS (Directly Observed Treatment, Short-course) regimen under the Revised National Tuberculosis Control Programme (RNTCP). The dosing of isoniazid, particularly in children, needs to be carefully considered to ensure efficacy while minimizing toxicity.

## **Why the Correct Answer is Right**
The correct dose of isoniazid for children in the DOTS regimen under RNTCP is **10 mg/kg/day**. This dosage is crucial for achieving therapeutic levels that effectively combat *Mycobacterium tuberculosis* while being mindful of potential side effects. Isoniazid works by inhibiting the synthesis of mycolic acid, an essential component of the mycobacterial cell wall.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 5 mg/kg/day - This dose is lower than the recommended dose and might not be as effective in treating tuberculosis.
- **Option B:** 15 mg/kg/day - This dose is higher than the recommended dose and could increase the risk of toxicity, including hepatotoxicity and neurotoxicity.
- **Option D:** 20 mg/kg/day - This is significantly higher than the recommended dose and would substantially increase the risk of adverse effects.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that isoniazid dosing in children should not exceed the adult dose, and it's often given as part of a combination therapy to prevent the development of drug resistance. The RNTCP guidelines are crucial for standardizing treatment protocols.

## **Correct Answer:** . 10 mg/kg/day